Image projection system

ABSTRACT

Apparatus is disclosed for projecting an image onto a display surface with varying degrees of magnification and having the capability of selectively projecting various portions of the image. This apparatus is capable of incorporating a plurality of different lenses and illustratively includes a reflective surface, which is movably mounted to increase or decrease the long conjugate distance between the lens and the display surface. The selected lens is inserted within the apparatus at its given focal distance from the transparency to be projected and is manipulated by a follow focus mechanism to maintain the projected image in focus as the reflected surface is being moved.

United States Patent [72] Inventor Robert P. Crandall Rochester, N.Y.

[21 Appl. No. 730,316

[22] Filed May 20, 1968 [45] Patented Sept. 14, 197] l 73] AssigneeEastman Kodak Company Rochester, N.Y.

[54] IMAGE PROJECTION SYSTEM 10 Claims, 12 Drawing Figs.

52 u.s.c| 353/76, 353/77, 353/99, 355/56, 355/57 511 lnt.Cl. -0031)21/22, 00313 21/28, G03b 27/34 [50] Field of Search 353/76, 77, 99;355/55,56,57,58,59, 60

Primary Examiner-Leonard Forman Assistant Examiner-Steven L. StephanAttorneys-Robert W. Hampton and R. Lewis Gable ABSTRACT: Apparatus isdisclosed for projecting an image onto a display surface with varyingdegrees of magnification and having the capability of selectivelyprojecting various portions of the image. This apparatus is capable ofincorporating a plurality of different lenses and illustrativelyincludes a reflective surface, which is movabiy mounted to increase ordecrease the long conjugate distance between the lens and the displaysurface. The selected lens is inserted within the apparatus at its givenfocal distance from the transparency to be projected and is manipulatedby a follow focus mechanism to maintain the projected image in focus asthe reflected surface is being moved.

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BY a w/ M ATTORNEYS pmm-lm 31604795 saw u or 4 SHORT CONJUGATE DISTANCE(mm) OI 1.- O COCO 3 a ROBERT P- CRANDALL mvsmox.

BY 4M 0 M ATTORNEYS L .CONJUGATE DISTANCE (mm) IMAGE PROJECTION SYSTEMCROSS-REFERENCES TO RELATED APPLICATIONS Reference is made to commonlyassigned copending US. Pat. application Ser. No. 730,443, entitled ImageProjection System, filed May 20, 1968 now US. Pat. No. 3,482,901 in thename of Charles J. Melech.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to image projection systems and more particularly to suchsystems for providing varying degrees of magnification of a projectedimage and capable of accepting various lenses to effect the desiredmagnification and projection of selected portions of the image.

The image projection system of the present invention is particularlyadapted for use with microfilm viewers or readers in which a selectedimage from an elongated strip of film may be chosen and projected withvarying degrees of magnification. Though this invention is describedwith regard to a microfilm reader, it is understood that the system ofthe present invention could be used with equal facility and advantage inother image projection systems, and therefore the following descriptionis provided for illustrative purposes only.

2. Description of the Prior Art One of the problems encountered in theprojection of selected images from a strip of microfilm is therequirement of flexibility in projecting images of varying size andvarying formats. It may be understood that documents of different sizesand formats may be photographed and the images recorded on a strip ofmicrofilm, which images are to be projected and examined by the operatorof a microfilm reader. Typically, it may be necessary to reorientate theimages so that the indicia is upright with respect to the observer andto magnify particular portions of an image so that the viewer may morereadily examine the stored information. frojection systems of the priorart as described in US. Pat. Nos. 2,746,344 and 3,181,416 provide forvarying degrees of magnification by providing a pair of mirrors whichare movable mounted upon an assembly between a lens and a displayscreen. A cam is associated with the mirror assembly to adjust theposition of a lens carriage upon which a lens is movably mounted. As thelong conjugate distance between the lens and the display screen isincreased by moving the mirror assembly, a corresponding readjustment ofthe position of the lens carriage and lens is made to maintain theprojected image in focus upon the display screen. The degree ofmagnification is dependent upon the long conjugate distance between thelens and the focal surface. There are practical limits to the size ofsuch projection systems, which in turn limit the degree of magnificationthat may be achieved by moving a pair of mirrors. Thus, it is desirableto incorporate a plurality of lenses within the projection system inorder to achieve varying degrees of magnification. When a high degree ofmagnification is desired, a lens with a relatively short focal lengthwould be inserted within the projection system and the projected imagewould be correspondingly magnified. Within US. Pat. No. 3,181,416, aprojection system is disclosed with a pair of lens that may bealternatively disposed in alignment to provide varying degrees ofmagnification. A plurality of cams are connected mechanically to acarriage supporting the mirror. The pair of lenses are disposed upon apivotably mounted member so that either lens may be inserted within theprojection path. A cam follower is associated with the pivotably mountedmember to be engaged with either of the two cams dependent upon whichlens is disposed within the projection system.

It would be desirable to incorporate one of a larger number of lenseseasily within the projection system to provide greater flexibility thanthe projection systems of the prior art. Further, it would be desired touse a single cam member and to provide a simple engagement with the cammember. The use of a plurality of cam members associated with the mirrorcarriage,

require that the cam follower be positively engaged with each of the cammembers. It would be desirable to simplify the mechanical connectionbetween the cam member and the assembly for mounting the plurality oflenses. In addition, the lens-mounting assembly should also beadjustable in a direction transverse to the length of microfilm so thatselected portions of the image may be projected onto the screen.

In order to change the degree of magnification, the reflective surfacesormirrors are moved to decrease or increase the long conjugate distancebetween the lens and the display screen. As the position of the mirrorsis being changed, it is necessary to impart a corresponding change inthe position of the lens to maintain the projected image in focus uponthe display screen. Most lenses require a follow focus correction whichis a nonlinear function of the movement of the mirrors. For shorter longconjugate focal distances, it is necessary to impart a great degree offollow focus correction to the lens than for greater long conjugatefocal distances. Nonlinear cam surfaces could be used to provide therequired nonlinear correction to the position of the lens. However, suchnonlinear surfaces would be difficult and expensive to machine, and itwould be desirable to provide rather simple cam surfaces to impart therequired follow focus adjustment to the lens.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide a new and improved image projection system capable of easilyincorporating a plurality of lenses to effect various degrees ofmagnification.

Another object of this invention is to provide a new and improved imageprojection system capable of effecting a follow focus correction foreach of a plurality of lenses to be inserted within the image projectionsystem.

A still further object of this invention is to provide a new andimproved image projection system capable of incorporating a plurality oflenses wherein each of the lenses may be easily adjusted along variousdimensions to achieve a fine focus of the projected image and also toselectively view various portions of an image.

A further object of this invention is to provide a new and improvedimage projection system in which the follow focus adjustment of the lensis effected by a relatively simple cam surface.

These and other objects are accomplished in accordance with theteachings of this invention by providing an image projection systemincluding a lens disposed upon an assembly adjustable along the path ofthe projected image, a reflecting surface disposed on a movable carriagebetween the lens and a focal surface, a cam associated with the mirrorcarriage and a suitable linkage disposed between the cam and the lenscarriage for providing an appropriate adjustment in the position of thelens to thereby maintain the projected image in focus upon the focalsurface. In one particular illustrative embodiment, the linkage includesa lever rotatably mounted upon a rod and flexibly biased to follow themovement of the cam. It is a significant aspect of a preferredembodiment of this invention that the cam connected to the mirrorcarriage presents a simple, linear surface which is skewed with respectto the rod to thereby provide a nonlinear rotation to the rod. In turn,the rod is connected to a lens-positioning cam which has a plurality ofgrooves or cam surfaces therein corresponding to each of the pluralityof lenses. The lens carriage is selectively engaged in the appropriategroove which translates the nonlinear rotational motion imparted theretointo a nonlinear motion along the path of the projected image to thelens to thereby compensate for the nonlinear optical characteristics ofthe lens.

In addition, the lens and lens carriage may be adjusted along the pathof the projected image by a fine focus control. More specifically, ashaft may be used for imparting a rotational motion from a control knobto a bearing disposed to exert a force upon a surface of thelens-positioning cam. The shaft may be threadably received by thebearing which is held in a nonrotating relationship with respect to thelens positioning cam. Thus, a motion along the path of the projectedimage may be imparted to the lens to achieve a fine focusing of theprojected image without interfering with the angular position of thelens positioning cam. In addition, the bearing may be so configured toallow the lens positioning cam to be disengaged from the lens carriageto thereby permit a new lens to be mounted upon the carriage and thecarriage to be in turn engaged with another groove of thelens-positioning cam. Further, a suitable brake may be applied to theshaft connected with the control knob to prevent the rotation impartedby the lens-positioning cam to the bearing to effect the angularposition of the fine focus control.

It is a significant aspect of a preferred embodiment of this invention,that the grooves of the lens-positioning cam be placed to determine thecorrect placement of the corresponding lens. More specifically, each ofthe plurality of lenses to be inserted within the image projectionsystem of this invention would normally have a different focal lengthwhich would determine the placement of the lens with regard to a stripof photographic film. Thus, when the lens carriage is engaged within oneof the grooves of the lens-positioning cam, the inserted lens issubstantially disposed at its focal length with respect to the strip offilm. In addition, the configuration of each of the grooves is sodetermined to provide the correct displacement along the path of theprojected image to the particular lens mounted upon the lens carriage.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and featuresof the present invention will become more apparent when considered inview of the following description and drawings in which:

FIG. 1 is an orthogonal view of an image projection system in accordancewith the teachings of this invention;

FIG. 2 is an orthogonal view of the lens and lens carriage assemblywhich is incorporated within the image projection system of FIG. 1;

FIGS. 3A and 3B are enlarged views of the lens support assembly whichmay be incorporated within the image projection system of FIG. 1;

FIGS. 4A and 4B are enlarged views of the cam follower assembly which isincorporated within the image projection system shown in FIG. 1;

FIG. 5 is an enlarged, orthogonal view of the brake incorporated withinthe image projection system of FIG. 1;

FIG. 6 is a sectional view and FIG. 7 is a plan view of the lenspositioning cam incorporated in the image projection system of FIG. 1;

FIGS. 8 and 9 are respectively a side view and an orthogonal view of thecarriage assembly upon which the mirrors are mounted, and the camassociated with this carriage assembly; and

FIG. 10 is a graph showing the required short conjugate distance oflenses to be incorporated within the projection system of FIG. 1 versusthe long conjugate distance, which is varied to increase or decrease themagnification of the projected image.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingsand in particular to FIG. 1, there is shown a variable magnificationimage projection system 10 including a source 14 of radiation forilluminating a selected frame of a filmstrip 12 and a lens 16 forfocusing the illuminated frame onto a display surface or screen 19. Thelens 16 is mounted upon a lens carriage assembly 18, which includes acarriage 20 movably mounted along a direction parallel to the projectedpath of the image, and a second carriage 26 movably supported along alinear path parallel to the width of the filmstrip 12. Morespecifically, the carriage 20 is mounted to slide upon a rod-shaped way24 which fits into a V-shaped slot 22 of the carriage 20. Similarly, thecarriage 26 is mounted to freely move upon a rod-shaped way 30 whichfits within a slot 28 (see FIG. 2) of the carriage 26.

As shown more clearly in FIG. 2, the carriage 26 may be selectivelymoved along a path parallel to the width of the filmstrip 12, by a knob42, which is connected to an elongated pinion gear 40. In turn, thepinion gear 40 meshes with a gear 38 which is connected through a shaft35 to a pinion gear 34. The use of the elongated pinion gear 40 allowsthe lens carriage assembly 18 to be moved axially along the path of theprojected image without disengaging the gear 38 from the pinion gear 40.The pinion gear 34 meshes with the teeth of a rack 32 attached to thecarriage 26 to thereby impart a linear motion to the carriage 26 along adirection parallel to the width of the filmstrip 12.

A prism assembly 46 is rotatably mounted upon a support bracket 44,which is in turn fixedly supported upon the carriage 26. The prismassembly 46 may in one illustrative embodiment take the form of a Dove"prism and be aligned in the path of the projected image. Such a prismassembly 46 would be rotated to in turn rotate the projected image. Abelt 48 is disposed in a frictional relationship about the prismassembly 46 and also about a pair of pulleys 47 and 49 rotatably mountedupon the support bracket 44,. As more clearly shown in FIG. 1, thepulley 49 is connected by a flexible shaft 50 to an adjusting knob 53.In order to allow for the movement of the carriage 20 along the path ofthe projectee image, the flexible shaft 50 is connected to the knob 53through a slotted member 51. More specifically, the flexible shaft 50 isslidably connected by a pin 52 in a slidable but nonrotationalrelationship to the member 51. As the knob 53 is rotated, acorresponding rotational motion will be imparted to the prism assembly46 thereby rotating the projected image. It may be understood thatcertain documents such as computer readout have type along the length ofthe document and will be photographed so that the long dimension of thedocument is disposed along the length of the strip 12. As a result, itwill be necessary to rotate the image of such a document approximatelyso that the type may be displayed upon the screen of this device in amanner that may be most easily read by the viewer.

The lens 16 is supported upon the carriage 26 by a mounting plate 127.As shown more clearly in FIGS. 3A and 3B, the lens 16 is removablysecured to the mounting plate 127 by a spring clip 128, which is itselfsecured to the plate 127 by a plurality of fasteners 126. The lens 16has a groove 132 disposed about its periphery. A lens flange 131 extendsnormally from the groove 132 and serves as a seating surface againstwhich the plate 127 is biased to thereby mount the lens 16 in an alignedrelationship with the filmstrip 12. The groove 132 of the lens 16 isdisposed within a V-shaped slot 129 of the plate 127. The spring clip128 has a pair of formed ends which flexibly fit over the center of thelens 16 to thereby secure the lens 16 within the slot 129. Further, theends 130 are flexibly disposed against a cam surface 133 associated withthe groove 132 so that the lens 16 is directed to the left (as shown inFIG. 3B) to thereby seat the flange 131 against the plate 127. Thus,there has been shown in FIGS. 3A and 38 an assembly into which aplurality of lenses may be interchangeably disposed.

With regard to FIG. 1, a pair of mirrors 62 and 64 are disposedin thepath of the projected image between the lens 16 and the display surfaceor screen 19. In order to vary the long conjugate distance between thelens 16 and the display surface 19 and therefore the magnification ofthe projected image, the mirrors 62 and 64 are disposed upon a mirrorcarriage assembly 54, which is movably mounted upon a pair of guide rods56 and 58 in a direction parallel to the incident path of the projectedimage from the lens 16. More specifically, the mirror carriage assembly54 is suspended from the guide rod 56 by a single bearing 57 and fromthe guide rod 58 by a pair of bearings 59 and 60. The mirrors 62 and 64are moved with a linear, bidirectional motion along the guide rods 56and 58 by a drive motor 66 which is connected to the carriage assembly54 by a chain or belt 68.

As the pair of mirrors 62 and 64 are moved to vary the long conjugatedistance, it is necessary to impart a corresponding adjustment to theplacement of the lens 16 to maintain the projected image in focus on thescreen 19. In order to maintain the projected image in focus, a cam 74is fixedly mounted upon the mirror carriage assembly 54. The cam 74 hasa surface or edge 76 which engages a follower lever 72. The lever 72 isfixedly secured to a follow focus rod 70, which is biased in acounterclockwise direction (as shown in FIG. 1) by a lever 78 fixedlysecured to the rod 70 and a spring 80. As seen in FIG. 1, a clockwiserotational motion is imparted to the lever 72 as the mirror carriageassembly 54 is moved towards the lens 16, and a counterclockwise motionis imparted to the lever 72 as the carriage 54 is moved away from thelens 16.

As shown in FIG. 6, the follow focus rod 70 is fixedly connected to alens-positioning cam 82 by a setscrew 88 so as to thereby impart arotational motion to the lens-positioning cam 82. With reference toFIGS. 1, and 7, a cam follower assembly 116 is fixedly secured to thelens support assembly 18 and in particular to the carriage 20, and isengageable with each of a plurality of cam grooves at surfaces 84, 85,86 and 87 disposed within the lens-positioning cam 82. Generally, thelens positioning cam 82 serves to convert the rotational motion impartedthereto by the lever 72 and the follow focus rod 70 into a motionapplied to the lens support assembly 18 along the path of the projectedimage. In particular, the cam grooves 84, 85, 86 and 87 are soconfigured to impart varying motions to the image support assembly 18corresponding to the different lenses that may be interchangeablymounted upon the assembly 18. As shown in FIG. 7, cam groove 87 has agreater pitch than the remaining grooves 84, 85 86 and therefore isadapted to take a lens of a longer focal length than the remaininggrooves. As will become evident later, it is a significant aspect ofthis invention that the cam grooves 84, 85, 86 and 87 are so spaced fromeach other so that when the cam follower assembly 116 is engaged in oneof the grooves, the corresponding lens 16 will be disposed at its focallength with respect to the strip 12.

A control knob 97 is provided to impart a fine focus adjustment to thelens 16. More specifically, the knob 97 is connected to a fine focus rod96, which is in turn connected to the lens position cam 82 to impart arectilinear motion to the lenspositioning cam 82. As shown in FIG. 6,the fine focus rod 96 has a threaded portion 98 threadably received by aspherically shaped bearing 100. The bearing 100 has a groove 101disposed parallel to the axis of the bearing 100 for receiving asetscrew 103 to secure the bearing 100 in a fixed, nonrotatingrelationship with respect to the lens-positioning cam 82. Upon the endof the fine focus rod 96 opposite the knob 97, there is disposed a stopwasher 102 to prevent the rod 96 from being rotated out of the bearing100. The lens-positioning cam 82 includes a centrally orientated bore 90for receiving the bearing 100 and a bore 92 of a smaller diameterthrough which the fine focus rod 96 is inserted to be threadablyreceived by the bearing 100. A bearing surface 94 is disposed betweenthe bores 90 and 92 to provide a surface against which the bearing Iabuts. A setscrew 104 is disposed within the lens-positioning cam 82 toabut the other side of the bearing 100. The surface 94 and the setscrew104 abut the bearing 100 to impart a rectilinear motion from the finefocus rod 96 to the lens-positioning cam 82. It is particularly notedthat the bearing 100 is spherically shaped so that the lens-positioningcam 82 may be depressed downwardly as shown in FIG. 6 or FIG. 1 so as tobe disengaged from the cam follower assembly 116 and to allow anotherlens 16 to be inserted within the image projection system 10.

As explained above, the lens 16 is adjusted to maintain the projectedimage in focus upon the screen 19 as the mirrors 62 and 64 are movedalong the guides 56 and 58 to effect the desired degree of imagemagnification. More particularly, a rotational motion is impartedthrough the follow focus rod 70 to the lens-positioning cam 82. In turn,the lens 16 is coupled by the cam follower assembly 116 to one of thecam grooves 84, 85, 86 or 87 of the lens-positioning cam 82. Each of thecam grooves 84, 85, 86 and 87 has a pitch calculated to apply thecorrect movement to the corresponding lens 16. In addition, theadjusting movement applied to lens 16 is partially dependent upon therotational movement of the bearing and the lens-positioning cam 82 aboutthe threaded portion 98 of the fine focus rod 96. It may be understoodthat as the cam 82 is rotated about the threaded portion 98, arectilinear movement will be imparted through the bearing I00 and thelenspositioning cam 82 to the selected lens 16. Therefore, the pitch ofthe grooves 84, 85, 86 and 87 is calculated to include the secondaryadjustment provided by the threaded portion 98.

With regard to FIGS. 1 and 5, a friction brake is disposed about thefine focus rod 96 to apply a sufiicient braking torque to prevent thebearing 100 from rotating the shaft 96 when the follow focus rod 70rotates the lens-positioning cam 82. The friction brake 110 has a pairof legs 112 and 113 forming a slot 111 therebetween. An adjusting bolt114 is disposed through the leg 112 to be threadably received by the leg113. As shown in FIG. 1, the fine focus rod 96 is disposed between thebite of the slot 111 and the adjusting bolt 114. By adjusting the bolt114, a suitable braking torque may be applied to the fine focus rod 96.A bolt 115 is disposed through the leg 113 to be positioned against aportion of the housing (not shown) of this device to prevent rotation ofthe friction brake 110. A spring 106 is disposed between the frictionbrake 110 and a front panel 108 through which the fine focus rod 96 isdisposed. The spring 106 exerts an axial force through the frictionbrake 110 upon the lens-positioning cam 82 to ensure the positiveengagement between the threaded portion 98 of the fine focus rod 96 andthe bearing 100 and to thereby eliminate any play in the fine focusadjustment when the knob 97 is turned. It may be understood that thefine focus rod 96 is fixed axially with respect to the front panel 108.

With regard to FIGS. 1, 4A and 4B, the cam follower assembly 116 isengageable with one of the grooves 84, 85, 86 and 87 of thelens-positioning cam 82 to translate the rotational motion of the cam 82to the lens carriage assembly 18. The cam follower assembly 116 includesa support member 118 having a horizontally extending arm 119 secured tothe lens carriage assembly 18, and a pair of vertically extending arms120 and 123. The cam follower assembly 116 includes a canted, flexiblemember 121 for releasably holding the lenspositioning cam 82 against thearm 120. The flexible member 121 is secured to the support member 118 bysuitable fasteners 122. A follower rod 124 is disposed between andfixedly held by the pair of vertically extending arms 120 and 123. Asshown in FIGS. 1 and 4A, the follower rod 124 is selectively engagedwith one of the grooves 84, 85 86 or 87 dependent upon the lens 16inserted within the system. As shown in FIG. 4B, the follower rod 124 isdisposed at an angle I with respect to a line normal to the member 121.As shown in FIG. 7, the grooves 84, 85, 86 and 87 are disposed at anincreasingly greater pitch with respect to the axis of thelens-positioning cam 82. The rod 124 is disposed with respect to the cam82 to mesh with the grooves 84, 85, 86 and 87. In particular, the angleDis selected as a compromise of the varying angles (or pitches) of thegrooves to be suitably coupled to all of these grooves.

In accordance with theteachings of this invention a plurality of lenses16 may each be inserted within the spring clip 128 upon lens carriageassembly 18 at a distance from the strip 12 determined by the grooves84, 85, 86 and 87. As shown most clearly in FIG. 2, a pointer 134 isfixedly secured to the mounting plate 127. A plate 136 is provided fordisplaying suitably spaced indicia 137 corresponding to the grooves 84,85 86 and 87. As mentioned above, the grooves 84, 85, 86 and 87 arespaced along the axis of the lens-positioning cam 82 distancescorresponding to the focal lengths of the lenses to be inserted withinthe spring clip 128. Thus, to ensure the engagement of the follower rod124 with the correct groove and at the same time to ensure the placementof the lens 16 at its focal length with respect to the filmstrip 12, thecam follower assembly 116 is engaged with one of the grooves 84, 85, 86

abutting against the lens-positioning cam 82. As shown in FIG.

1, the winged portions 142 prevent the projection 140 from beingdisposed within one of the grooves of the lens-positioning cam 82. Bydepressing the lever 138, the follower rod 124 is disengaged from one ofthe grooves 84, 85, 86 and 87 to thereby allow the lens carriageassembly 18 to be rectilinearly slid along the way 24. The assembly 18and in particular the carriage 20 is slid until the pointer 134coincides with a particular one of the indicia 137 corresponding to thelens 16 to be insertedwithin the spring clip 128. A lens 16 so insertedwill be matched with its correct cam groove and also disposed at itsfocal length with respect to the strip 12.

There is shown in FIG. 10 the optical characteristics of severallensesthat may be incorporated within the image projection system 10 of thisinvention. Particular reference is made'to the above-identifiedcopending application of Charles .I. Melech, which describes aparticular objective and associated lens system that may be used withthe image projection system 10 described herein. As described above withreference'to FIG. 1, an adjustment is made in the position of the lens16 with regard to the strip 12 to compensate for the movement ofthemirrors 62 and 64 and to maintain the projected image-in focus upon thedisplay screen 19. The distance between the optical center of the lens16 and the surface of strip 12 is defined as the short conjugatedistance, whereas the distance between the optical center of the lens 16and the display screen 19 may be defined as the long conjugate distance.

FIG. 10 presents a series of curves I, II and IH demonstrating v therequired short conjugate distance to maintain the projected imagefocused upon adisplay screen disposed at varying long conjugatedistances.

As explained above, the mirrors 62 and 64 may be moved uponthe mirrorcarriage assembly 5410 thereby increasethe long conjugate distance of,the system. To maintain the projectedfimage in focus, a correspondingchange in the short conjugate distance must be made as determined by thecurves of FIG. 10, In accordance with the teachings of this invention,the cam-74 afiixed torthe mirror carriageassembly 54 imparts arotational motion to the follow focus rodj70 through the lever 72. Asthe mirror carriage assembly 54 is driven linearly by the motor 66along'a rectilinear path parallel to the rod 70, the cam surface 76engages various portions of the lever 72 to thereby impart a rotationalmotion to the lever 72 and the rod 70 With regard to FIG. 10, it isapparent that the curves are nonlinear and that varying amounts ofadjustment must be imparted to the lens 16 depending upon the longconjugate distance of the system. For greater long conjugate distances,smaller amounts of correction are required. As the long conjugatedistance decreases, (corresponding to the disposition of the assembly 54closer to the lens 16), the amount of adjustment to .be imparted to theposition of the lens 16 increases. A nonlinear follow focus movementcould be provided by making the cam surface 76 of a suitable nonlinearconfiguration, and/or by making the cam surfaces 84, 85, 86 and 87 ofthe lens-positioning cam 82 with nonlinear pitches. Such operations aredifficult and expensive to perform. and in a preferred embodiment ofthis invention, a nonlinear follow focus movement is achieved by formingthe cam surface 76 into a straight edge which is skewed with respect toan axis 75 of the rod 70.

As shown in FIGS. 8 and 9, the lever 72 is brought into contact with thecam surface 76 at a point 73. As a result of the configuration anddisposition of the cam surface 76, the distance between the point 73 ofcontact and the axis 75 changes as the carriage 54 is moved with respectto the lens 16. The point 73 is shown in FIG. 9 to be an X-distance fromthe axis 75. As the assembly 54 is moved toward the lens 16, the lever72 assumes a first position 172 (shown in phantom) with a point ofcontact 173 and then a second position 272 with a corresponding point273 of contact. As readily seen, the distance Y between the point 173and the axis 75 is less than the distance X, and the distance Z betweenthe point 273 and the axis 75 is less than the distance Y. As thedistance between the point of contact of the lever 72 with cam surface76 becomes smaller, a greater angular rotation is imparted to the rod 70for a given, linear movement of the mirrorcarriage assembly 54. Inaccordance with the teachings of this invention, the nonlinear movementimparted by the rod 70 through the lens-positioning 'cam 82 to the lens16 is calculated to substantially provide the nonlinear, follow focusmovement dictated by the curves of FIG. 10. The nonlinear, follow focusmovement is determined by the distance between the points 73, 173 and273, and the axis 75. More specifically, the degree of nonlinearity ofthe follow focus movement will be increased by increasing the differencebetween the distances of points of contact and the axis 75 at both endsof the cam surface 76 for a cam 74 of a given length. In other words,the nonlinearity of a cam 74 of fixed length may be increased byincreasing the differences between the distance X and distance 2 asshown in FIG. 9.

Thus, there has been shown an image projection system capable ofprojecting an image with variable degrees of magnification whilemaintaining the image in focus upon the focus surface by the use of acam member of simple configuration. The system of this invention iscapable of incorporating a plurality of lenses each of which is kept infocus while the magnification of the system is changed and which iseasily disposed in the system at its focal length from the image to beprojected. In addition, the system of this invention provides for a finefocus adjustment of the lens without disturbing the follow focusmechanism, and further allows for the selection of various portions ofthe image to be projected and for the rotation of the image so that itmay be more easily observed.

This invention has been described in detail with reference to apreferred embodimennbut it will be understood that variations andmodifications can be effected within the spiritand scope ,of theinvention as described hereinabove and as defined the appended claims.

We claim: j Y

1. An image projection system for projecting an image from aninformation bearing medium onto a surface including; means forinterchangeably incorporating a plurality of lenses, reflectingmeansdisposed to direct the image derived from one of the plurality oflenses onto the surface, meanslfor selectively varying the position ofsaid reflecting means'tovary the long conjugate distance between the onelens and said surface, and follow focus means responsive to the positionof said reflecting means to vary the position of said support means andsaid one lens to substantially maintain the image in focus upon thesurface, said follow focus means including a first cam member affixed tosaid reflecting means, a second cam member having a camming surfacecorresponding to each of the plurality of lenses a lever disposed tofollow the motion of said first cam member, and rod means fortransferring said motion from said lever to said second cam member.

2. An image projection system as claimed in claim 1, wherein said rodmeans is flexibly biased to engage said lever with said firstcam member.

3. An image projection system as claimed in claim 1, which additionallyincludes fine focus means associated with said follow focus means forfurther adjusting the position of the incorporated one of the pluralityof lenses to ensure that the image is in focus upon the surface, saidfine focus means including a bearing having a threaded portion forimparting rectilinear motion to said camming surfaces of said second cammember and a rotatable member having a threaded portion which isthreadably received by said bearing, said bearing having a surface ofsubstantially spherical configuration for allowing said follow focusmeans to be disengaged from said means for interchangeably incorporatinga plurality of lenses.

4. A system for projecting an image from an object onto a focal surfaceincluding; a first-carriage for interchangeably receiving a plurality oflenses, a second carriage including at least one reflective surface fordirecting the image onto the focal surface, a cam member secured to saidsecond carriage, said first and second carriages being movably mountedwith respect to the object, and a follow focus system responsive to theposition of said second carriage for varying the position of said firstcarriage to maintain the projected image in focus upon the focalsurface, said follow focus system including, lens-positioning meanscooperably connected to said first car- 'riage and having a cammingsurface corresponding to each one of the plurality of lenses forpositioning the corresponding lens with respect to the object and forcontrolling the movement of said first carriage when one of theplurality of lenses is incorporated within said system, a lever flexiblybiased against said cam member, and a follow focus rod to which saidlever is secured, said follow focus rod being connected to saidlenspositioning means to impart rotational motion to saidlenspositioning means.

5. An image projection system for projecting an image from an objectonto a focal surface, comprising support means for interchangeablyincorporating a selected lens from a plurality of lenses, reflectingmeans for directing the image onto the focal surface, means forselectively varying the position of said reflecting means to vary thelong conjugate distance between the selected lens and the focal surface,and a follow focus system including a first cam member atfixed to saidsupport means, a lever for following the movement of said first cammember, a second cam member, and a linking member for coupling saidfirst and second cam members, said second cam member having a camsurface for each of the plurality of lenses for providing a follow focusmovement corresponding to the selected lens incorporated with saidsystem for projecting.

6. An image projection system as claimed in claim 5, wherein each ofsaid cam surfaces is disposed a distance from the objecttoensure thatthe image is substantially in focus upon the focalsurface when theselected lens is incorporated within said system for projecting.

7. An image-projecting system as claimed in claim 6, whereinsaiddistance is approximately equal to the focal length of the selectedlens.

8. An image-projecting system as claimed in claim 7, wherein saidsupport means includes a member which is selectively engageable with oneof the cam surfaces.

9. Apparatus for projecting an image onto a focal surface, saidapparatus including:

a. lens means;

b. means movably mounted with respect to said lens means for varying thelong conjugate distance between said lens means and the focal surface;

c. drive means for imparting a first displacement along a rectilinearpath to said means for varying; and

d. follow focus means responsive to the first displacement of said meansfor varying for imparting a second displacement as a nonlinear functionof the first displacement to i said lens means to maintain the image infocus upon the focal surface, said follow focus means including a cammember affixed to said means for varying and having a cam surface and amember rotatably mounted about an axis, said last mentioned member beingbiased to follow the movement of said cam surface, said surfaceincluding a straight line skewed with respect to said axis.

10. An image projection system as claimed in claim 9, wherein saidstraight line is so skewed with respect to said axis that the distancebetween said straight line and said axis decreases as a function of thedistance from said lens means.

1. An image projection system for projecting an image from aninformation bearing medium onto a surface including; means forinterchangeably incorporating a plurality of lenses, reflecting meansdisposed to direct the image derived from one of the plurality of lensesonto the surface, means for selectively varying the position of saidreflecting means to vary the long conjugate distance between the onelens and said surface, and follow focus means responsive to the positionof said reflecting means to vary the position of said support means andsaid one lens to substantially maintain the image in focus upon thesurface, said follow focus means including a first cam member affixed tosaid reflecting means, a second cam member having a camming surfacecorresponding to each of the plurality of lenses a lever disposed tofollow the motion of said first cam member, and rod means fortransferring said motion from said lever to said second cam member. 2.An image projection system as claimed in claim 1, wherein said rod meansis flexibly biased to engage said lever with said first cam member. 3.An image projection system as claimed in claim 1, which additionallyincludes fine focus means associated with said follow focus means forfurther adjusting the position of the incorporated one of the pluralityof lenses to ensure that the image is in focus upon the surface, saidfine focus means including a bearing having a threaded portion forimparting rectilinear motion to said camming surfaces of said second cammember and a rotatable member having a threaded portion which isthreadably received by said bearing, said bearing having a surface ofsubstantially spherical configuration for allowing said follow focusmeans to be disengaged from said means for interchangeably incorporatinga plurality of lenses.
 4. A system for projecting an image from anobject onto a focal surface including; a first carriage forinterchangeably receiving a plurality of lenses, a second carriageincluding at least one reflective surface for directing the image ontothe focal surface, a cam member secured to said second carriage, saidfirst and second carriages being movably mounted with respect to theobject, and a follow focus system responsive to the position of saidsecond carriage for varying the position of said first carriage tomaintain the projected image in focus upon the focal surface, saidfollow focus system including, lens-positioning means cooperablyconnected to said first carriage and having a camming surfacecorresponding to each one of the plurality of lenses for positioning thecorresponding lens with respect to the object and for contrOlling themovement of said first carriage when one of the plurality of lenses isincorporated within said system, a lever flexibly biased against saidcam member, and a follow focus rod to which said lever is secured, saidfollow focus rod being connected to said lens-positioning means toimpart rotational motion to said lens-positioning means.
 5. An imageprojection system for projecting an image from an object onto a focalsurface, comprising support means for interchangeably incorporating aselected lens from a plurality of lenses, reflecting means for directingthe image onto the focal surface, means for selectively varying theposition of said reflecting means to vary the long conjugate distancebetween the selected lens and the focal surface, and a follow focussystem including a first cam member affixed to said support means, alever for following the movement of said first cam member, a second cammember, and a linking member for coupling said first and second cammembers, said second cam member having a cam surface for each of theplurality of lenses for providing a follow focus movement correspondingto the selected lens incorporated with said system for projecting.
 6. Animage projection system as claimed in claim 5, wherein each of said camsurfaces is disposed a distance from the object to ensure that the imageis substantially in focus upon the focal surface when the selected lensis incorporated within said system for projecting.
 7. Animage-projecting system as claimed in claim 6, wherein said distance isapproximately equal to the focal length of the selected lens.
 8. Animage-projecting system as claimed in claim 7, wherein said supportmeans includes a member which is selectively engageable with one of thecam surfaces.
 9. Apparatus for projecting an image onto a focal surface,said apparatus including: a. lens means; b. means movably mounted withrespect to said lens means for varying the long conjugate distancebetween said lens means and the focal surface; c. drive means forimparting a first displacement along a rectilinear path to said meansfor varying; and d. follow focus means responsive to the firstdisplacement of said means for varying for imparting a seconddisplacement as a nonlinear function of the first displacement to saidlens means to maintain the image in focus upon the focal surface, saidfollow focus means including a cam member affixed to said means forvarying and having a cam surface and a member rotatably mounted about anaxis, said last mentioned member being biased to follow the movement ofsaid cam surface, said surface including a straight line skewed withrespect to said axis.
 10. An image projection system as claimed in claim9, wherein said straight line is so skewed with respect to said axisthat the distance between said straight line and said axis decreases asa function of the distance from said lens means.